Cloud computing, machine-to-machine, 3D formats, Audio and Video on Demand (AVOD) and mobility are some of the services, which have led to a rising demand for bandwidth. In this context, Full Service Access Network (FSAN) Group and International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) have started to investigate new technologies for Next-Generation Passive Optical Networks 2 (NG-PON2). The main goal is to increase the bandwidth beyond the current 10 Gb/s downstream and 2.5 Gb/s upstream in the optical access network.
Among all the proposals, Time- and Wavelength-Division Multiplexed-PON (TWDM-PON) has stood out. In TWDM-PON, the aggregate rate is obtained by stacking several 10 Gigabit-PONs (XG-PONs), using different pairs of wavelength (upstream wavelength, downstream wavelength). For the concrete case where four XG-PONs are stacked, 40 Gb/s downstream and 10 Gb/s upstream are reached, i.e., four times the aggregate rate of the current PON.
The major challenges of planning this new architecture are the PONs coexistence and the equipment/infrastructure re-use. The spectrum is already occupied for other technologies, such as G-PON, XG-PON and Video. Therefore, the TWDM-PON has to take free spectrum bands in order to not interfere with other PONs. Besides, the TWDM-PON deployment cannot obligate to a total replacement of the already existing infrastructure. Efforts have to be made in the sense of re-using the existing equipment and infrastructures. This will cause a significant reduction of the costs.
The Photonic Integration will represent a huge break-through in terms of costs, since this will lead to higher density and lower power consumption. Several materials have been studied for photonic integration. Some of them are Silicon on Insulator (SOI), Silicon Nitride (Si3N4), Silicon Dioxide (SiO2) and Indium phosphide (InP).
Taking all this in consideration, having a monolithic photonic integrated circuit, which comprises a TWDM-PON transmitter and is also capable of supporting all the current technologies, is a worth challenge.